The present invention relates to automatic arc welding methods of the type employing a consumable or non-consumable electrode which is moved along the direction of the weld line of a welding joint, and more particularly the invention relates to an arc welding method so designed that under a unattended operating condition, a welding electrode is reciprocated or oscillated in the width direction within the groove and simultaneously the movement of the electrode in the vertical or upright direction is controlled so as to always maintain the arc length constant.
To realize an unattended automatic welding, it is necessary to use a torch sensor and a torch position adjusting mechanism for automatically sensing and controlling the torch position with respect to the two dimensional deviation of the groove line which varies from instant to instant during the welding operation.
In the past, various sensors of the above type have been used and they include the contact types, such as, the differential transformer, potentiometer and limit switch types and the non-contact types, such as, the electromagnetic and optical position detecting types. However, since the use of these sensors requires that a sensor or a specific device be positioned near the torch in any case, it is necessary to maintain a predetermined distance between the sensing position and the controlled system position due to the dimensional limitation and it has been possible to realize only such control systems which have a limited accuracy despite its complicated construction in which the torch position is controlled by providing the sensor output with a time differential corresponding to the dimension of the spacing.
Further, the automatic welding requires the automatic control of welding conditions in accordance with variations in conditions such as the shape of the groove and it has mostly been the practice to effect the desired adjustment, setting and control through manual operations. Same methods have been proposed in which the groove width in the front of the arc is detected by means of electromagnetic induction, the reflection of light or the like so as to feedback control the welding conditions, and the control by such method is also limited by the fact that the true groove cross-section is not evident, although it is possible to detect the width of the groove. Practically, there has been no groove cross-section detecting method which is suited for automation, and anyway the above-mentioned sensing means not only involve a deviation of the sensing position from the arc position but also require the use of separate sensors for the previously mentioned tracing purposes and the welding condition controlling purposes, thus making it extremely difficult to realize a system capable of accurate control.